Silver halide multilayer color photographic elements usually comprise, coated on a support, three silver halide dye-forming units or layers sensitive to blue, green and red light respectively associated with yellow, magenta and cyan dye-forming couplers. Preferably the elements comprise non-diffusible couplers which are incorporated in each of the light sensitive layers. These elements additionally comprise other non-light sensitive layers, such as intermediate layers, filter layers, antihalation layers and protective layers, thus forming a multilayered structure. These color photographic elements, after imagewise exposure to actinic radiation, are processed in a chromogenic developer to yield a visible color image.
Generally, with respect to the blue light sensitive layer, the inherently blue light sensitive region of the silver halides is normally utilized as it is. There may be the need, however, of increasing the absorption of light of given wavelenghths within the sensitivity spectrum of the emulsion, in order to enhance the record of the corresponding color and improve the response of the film in terms of color purity. To solve this problem, the blue-sensitive emulsion layer may be spectrally sensitized with the addition of spectral sensitizing dyes to impart thereto an absorption characteristic in a different, usually longer, wavelength region. However, the addition of spectral sensitizing dyes to a blue-sensitive silver halide emulsion may have the negative effect of decreasing the overall sensitivity of the emulsion to blue light.
Another problem often related to a blue-sensitive silver halide emulsion is the fading of the latent image. The latent image in a silver halide emulsion consists of minute specks of metallic silver formed in the interior or on the surface of individual silver halide grains upon exposure to actinic radiation. Development of exposed silver halide elements will selectively reduce to metallic silver those silver halide grains containing a latent image speck above a threshold size. It is known that a latent image is not permanent and, over a period of time, it fades with a consequent loss in image density and speed.
Among the latent image stabilizers for silver halide emulsions known in the art are N-alkenyl benzothiazolium and naphthothiazolium salts described in U.S. Pat. No. 3,954,478 and previously known as antifoggants in DE Pat. No. 867,355, compounds obtained by alkaline hydrolysis of said salts described in U.S. Pat. No. 4,423,140, compounds obtained by hydrolysis of certain thiazolium salts described in U.S. Pat. No. 4,374,196 and 2-unsubstituted N-alkenyl thiazolium salts described in U.S. Pat. No. 4,780,400. Problems are encountered with the use of these types of image stabilizers in blue-sensitive layers containing spectrally sensitized silver halide emulsions. These problems relate to a reduction of sensitivity. There is, therefore, the need to provide compounds or combination of compounds which give high sensitivity and good latent image stabilization to blue light sensitive layers as well as to other sensitive silver halide photographic emulsion layers.